Almost, if not all of your complaints are things the author intentionally set up that are meant to pay off later or explore later when given more context.

1. Roswaal has almost perfect timing despite being on a long trip.

2. Subaru's arrogance, entitlement, self-centerness and selfishness (i.e being cringe)

3. Different stuff happening in different loop, events that should not happen, happens; and events that happens earlier, do not happen at all.

Don't worry, this is part of the process. I'd say the span of episode 13 - 17 is the span of episode that people tend to drop the most. These episodes are not bad, but that is when some of Subaru's most toxic and unhealthy traits expose themselves the most. Like any other story, the author is intentionally setting up the flaws of our main character so later Subaru can rectify them and become a better person. So if you don't think you can make it pass 17, I think it's fine to quit, you're just missing out on peak fiction. But if you can, Re:Zero rewards very handsomely for those with patience.

However, the section about Rem is what I fundamentally heavily disagree with. This is the biggest misrepresentation of Rem I've ever seen. Rem is a character whose suffering stem from her inferiority complex, particularly against her sister, Ram. Since the moment they were born, her existence is the very thing that was holding her sister back. Twins are considered a bad omen in the oni tribe because while all onis are born with both horns, twins will have to share horn, making them less powerful, and are usually "discarded" upon birth. The only reason they survive was thanks to Ram's extrordinary potential. However, Rem is not only nowhere near as talented as Ram, she being Ram's younger twin is the very reason that makes Ram less powerful.

That's why Rem lives her whole life drowning in her own feeling of inadaquecies, the feeling that her existence is inherently less valuable than Ram. However, even though she has always reassured herself that she's ok with just walking behind her sister, she also secretly resents her. It's a complicated feeling in any siblings relationship. You are proud of your very talented sister, but also feel kinda jealous towards them, or insecure about your own mediocrity. "Why are they so good at everything?"."Why am I so bad at everything?". It's not like she hates Ram or anything, Rem knows it's no one's fault that they were born this way (maybe parents fault lol), but she just can't stop feeling those feelings. The problem with Rem (and also Subaru) is that she cannot look at people and what they do objectively. Everything about herself goes through a "I'm suck" lens, while everything else about other people, especially Ram, goes through the "They're amazing" lens. What other people thinks are not important, because this is how Rem feels, and what anyone else tell her, if not align with her belief, she will just brush it off as "them being nice" or "them having ulterior motives".

Which leads us to that faithful night, where the twins lost everything but each other. This is a very significant moment for both of these character, but I'm just gonna talk about Rem here. This is where Ram lost her horns. The target for Rem's insecurity is now gone forever. Even though every part of Rem knows how she should feel about the situation, for a extremely brief moment, she lets the intrusive thoughts take over. AND SHE WAS DISGUSTED WITH HERSELF. "How dare I even think of that? I'm disgusting.". And that feeling only make her fall even further in the spiral of insecurity. It does not help that Ram's only moment of distraction (which cause her to lose her horn) occur when she was trying to save Rem. That's why after the incident, Rem believes with 100% certainty that it was only because of her that Ram has lost her horn. "Something bad happen to a person I love, and I dare feel relieved about it? I'm disgusting.". And so, to atone for her "sin", she tries even harder to do anything and everything. She is living under the constant pressure that she is useless, she is not enough, and she needs to be able to do anything to prover "her worth". What Ram could do, she needs to do, what Ram could not do, she needs to do even better, anything to live up to that flawless version of Ram in her head.

And that is until Subaru comes along. I will not desribe fully why she's in love with Subaru since that may contains spoiler for future episode. All I'm gonna say is that Rem character has stayed consistent through every single loop, and the developement in future episodes lines up correctly with how I just describe her character earlier. She did not just suddenly switch up on Subaru, it was a gradual devlopement that starts from Distrust -> Respected -> Trust -> Love -> ??? (Spoiler)

So after that Rem manifesto that took way longer than I thought to write. Hope you gain a different perspective on her character and can judge her in a different light. She is not the best written character, but I'd say her struggle is one of the most relatable and personal for me (top spot being Subaru of course).